Drive systems for bicycles typically comprise a pair of rotating pedal cranks connected to the rear wheel of the bicycle by a chain and sprockets. Although these systems have been found useful, they also have inherent disadvantages. In particular, the tangential force exerted on the pedals by the cyclist varies considerably depending upon the relative position of the pedal cranks, the force generally being at a maximum only when the pedal cranks are approximately horizontal. This not only limits efficiency, but also the maximum power output of the cyclist.
Another approach utilizes a drive system having a drive link coupled by bearings to a crank and a tie rod. Drive forces are then transmitted by a cyclist from the drive link, through the crank, to the wheels of a bicycle. A system of this general description is provided, for example, in DE 4404831 A. A further conventional drive mechanism for bicycles has pedals attached to racks mounted for reciprocating movement. Such a mechanism is disclosed, for instance, in WO 96/22911.